Merge branch 'master' into groupby-plot

* master: (458 commits)
  Add units if "unit" is in the attrs. (pydata#4850)
  speed up the repr for big MultiIndex objects (pydata#4846)
  dim -> coord in DataArray.integrate (pydata#3993)
  WIP: backend interface, now it uses subclassing  (pydata#4836)
  weighted: small improvements (pydata#4818)
  Update related-projects.rst (pydata#4844)
  iris update doc url (pydata#4845)
  Faster unstacking (pydata#4746)
  Allow swap_dims to take kwargs (pydata#4841)
  Move skip ci instructions to contributing guide (pydata#4829)
  fix issues in drop_sel and drop_isel (pydata#4828)
  Bugfix in list_engine (pydata#4811)
  Add drop_isel (pydata#4819)
  Fix RST.
  Remove the references to `_file_obj` outside low level code paths, change to `_close` (pydata#4809)
  fix decode for scale/ offset list (pydata#4802)
  Expand user dir paths (~) in open_mfdataset and to_zarr. (pydata#4795)
  add a version info step to the upstream-dev CI (pydata#4815)
  fix the ci trigger action (pydata#4805)
  scatter plot by order of the first appearance of hue (pydata#4723)
  ...

.coveragerc

@@ -1,7 +1,7 @@
 [run]
 omit =
-    xarray/tests/*
-    xarray/core/dask_array_compat.py
-    xarray/core/npcompat.py
-    xarray/core/pdcompat.py
-    xarray/core/pycompat.py
+    */xarray/tests/*
+    */xarray/core/dask_array_compat.py
+    */xarray/core/npcompat.py
+    */xarray/core/pdcompat.py
+    */xarray/core/pycompat.py

.github/ISSUE_TEMPLATE/bug-report.md

@@ -0,0 +1,39 @@
+---
+name: Bug report
+about: Create a report to help us improve
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+<!-- Please include a self-contained copy-pastable example that generates the issue if possible.
+
+Please be concise with code posted. See guidelines below on how to provide a good bug report:
+
+- Craft Minimal Bug Reports: http://matthewrocklin.com/blog/work/2018/02/28/minimal-bug-reports
+- Minimal Complete Verifiable Examples: https://stackoverflow.com/help/mcve
+
+Bug reports that follow these guidelines are easier to diagnose, and so are often handled much more quickly.
+-->
+
+**What happened**:
+
+**What you expected to happen**:
+
+**Minimal Complete Verifiable Example**:
+
+```python
+# Put your MCVE code here
+```
+
+**Anything else we need to know?**:
+
+**Environment**:
+
+<details><summary>Output of <tt>xr.show_versions()</tt></summary>
+
+<!-- Paste the output here xr.show_versions() here -->
+
+
+</details>

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,8 @@
+blank_issues_enabled: false
+contact_links:
+  - name: Usage question
+    url: https://github.com/pydata/xarray/discussions
+    about: |
+      Ask questions and discuss with other community members here.
+      If you have a question like "How do I concatenate a list of datasets?" then
+      please include a self-contained reproducible example if possible.

.github/ISSUE_TEMPLATE/feature-request.md

@@ -0,0 +1,22 @@
+---
+name: Feature request
+about: Suggest an idea for this project
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+<!-- Please do a quick search of existing issues to make sure that this has not been asked before. -->
+
+**Is your feature request related to a problem? Please describe.**
+A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
+
+**Describe the solution you'd like**
+A clear and concise description of what you want to happen.
+
+**Describe alternatives you've considered**
+A clear and concise description of any alternative solutions or features you've considered.
+
+**Additional context**
+Add any other context about the feature request here.

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,6 +1,7 @@
 <!-- Feel free to remove check-list items aren't relevant to your change -->
 
- - [ ] Closes #xxxx
- - [ ] Tests added
- - [ ] Passes `isort -rc . && black . && mypy . && flake8`
- - [ ] Fully documented, including `whats-new.rst` for all changes and `api.rst` for new API
+- [ ] Closes #xxxx
+- [ ] Tests added
+- [ ] Passes `pre-commit run --all-files`
+- [ ] User visible changes (including notable bug fixes) are documented in `whats-new.rst`
+- [ ] New functions/methods are listed in `api.rst`

.github/actions/detect-ci-trigger/action.yaml

@@ -0,0 +1,29 @@
+name: Detect CI Trigger
+description: |
+  Detect a keyword used to control the CI in the subject line of a commit message.
+inputs:
+  keyword:
+    description: |
+      The keyword to detect.
+    required: true
+outputs:
+  trigger-found:
+    description: |
+      true if the keyword has been found in the subject line of the commit message
+    value: ${{ steps.detect-trigger.outputs.CI_TRIGGERED }}
+runs:
+  using: "composite"
+  steps:
+    - name: detect trigger
+      id: detect-trigger
+      run: |
+        bash $GITHUB_ACTION_PATH/script.sh ${{ github.event_name }} ${{ inputs.keyword }}
+      shell: bash
+    - name: show detection result
+      run: |
+        echo "::group::final summary"
+        echo "commit message: ${{ steps.detect-trigger.outputs.COMMIT_MESSAGE }}"
+        echo "trigger keyword: ${{ inputs.keyword }}"
+        echo "trigger found: ${{ steps.detect-trigger.outputs.CI_TRIGGERED }}"
+        echo "::endgroup::"
+      shell: bash

.github/actions/detect-ci-trigger/script.sh

@@ -0,0 +1,47 @@
+#!/usr/bin/env bash
+event_name="$1"
+keyword="$2"
+
+echo "::group::fetch a sufficient number of commits"
+echo "skipped"
+# git log -n 5 2>&1
+# if [[ "$event_name" == "pull_request" ]]; then
+#     ref=$(git log -1 --format='%H')
+#     git -c protocol.version=2 fetch --deepen=2 --no-tags --prune --progress -q origin $ref 2>&1
+#     git log FETCH_HEAD
+#     git checkout FETCH_HEAD
+# else
+#     echo "nothing to do."
+# fi
+# git log -n 5 2>&1
+echo "::endgroup::"
+
+echo "::group::extracting the commit message"
+echo "event name: $event_name"
+if [[ "$event_name" == "pull_request" ]]; then
+    ref="HEAD^2"
+else
+    ref="HEAD"
+fi
+
+commit_message="$(git log -n 1 --pretty=format:%s "$ref")"
+
+if [[ $(echo $commit_message | wc -l) -le 1 ]]; then
+    echo "commit message: '$commit_message'"
+else
+    echo -e "commit message:\n--- start ---\n$commit_message\n--- end ---"
+fi
+echo "::endgroup::"
+
+echo "::group::scanning for the keyword"
+echo "searching for: '$keyword'"
+if echo "$commit_message" | grep -qF "$keyword"; then
+    result="true"
+else
+    result="false"
+fi
+echo "keyword detected: $result"
+echo "::endgroup::"
+
+echo "::set-output name=COMMIT_MESSAGE::$commit_message"
+echo "::set-output name=CI_TRIGGERED::$result"

.github/stale.yml

@@ -56,4 +56,4 @@ limitPerRun: 1  # start with a small number
 
 # issues:
 #   exemptLabels:
-#     - confirmed
+#     - confirmed